Known prior art plasticizers for polymers include but are not limited to esters that are reaction products of 1) aliphatic or aromatic mono- and dicarboxylic acids with 2) mono- and dihydric alcohols or glycols. Typical plasticizers for vinyl chloride polymers include esters of benzoic acid with monomeric or oligomeric glycols and esters of phthalic acid with monohydric alcohols.
U.S. Pat. Nos. 6,652,774; 6,740,254; and 6,811,722, describe mixed esters of glycerol as phthalate-free plasticizers for resinous polymers, including vinyl polymers, rubbers, polyurethanes and acrylics. At least one of the esters in the mixture exhibits the general formula CH2(OOR1)CH(OOR2)CH2(OOR3) wherein at least two of R1, R2 and R3 are different alkyl groups. In preferred embodiments R1, R2 and R3 contain up to 11 carbon atoms each, preferably from 2 to about 11 carbons each.
The ester compositions described in the aforementioned patents are mixtures prepared by reacting a mixture of at least two carboxylic acids with glycerol. The types and relative concentrations of the individual esters in the resultant mixtures vary from batch to batch. This variation makes it difficult to predict the composition of a particular batch or the level of plasticization that would be imparted to a polymer by that batch and, more importantly, the concentration of a particular batch of plasticizer required to achieve a desired degree of plasticization.
U.S. Pat. No. 5,444,110, describes crosslinkable plastisols wherein the polyvinyl chloride resin contains epoxy groups. The specification of this patent contains a listing of over 100 esters commonly used as plasticizers.